Investments Distribution by External Credit Rating for Fixed Maturity Securities (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale
Fixed Maturity Securities	$ 33,056.6	$ 35,629.9
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	822.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 2,506.7
Fixed maturity securities in unrealized loss position percent of total	100.00%
External Credit Rating, Investment Grade
Debt Securities, Available-for-sale
Fixed Maturity Securities	$ 31,848.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	793.9
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 2,458.0
Fixed maturity securities in unrealized loss position percent of total	98.10%
External Credit Rating, Below-Investment-Grade
Debt Securities, Available-for-sale
Fixed Maturity Securities	$ 1,208.6
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	28.1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 48.7
Fixed maturity securities in unrealized loss position percent of total	1.90%